1. Field of the Invention
The present invention relates to a nonvolatile storage device such as a semiconductor memory card including a nonvolatile memory and a memory controller controlling the nonvolatile memory, an access device that accesses the nonvolatile storage device, and a nonvolatile storage system using the nonvolatile storage device and the access device.
2. Description of the Related Art
A demand has recently grown for nonvolatile storage devices including a writable nonvolatile memory, primarily for semiconductor memory cards. The semiconductor memory cards are more expensive than optical disks and tape media.
However, the significant merits of semiconductor memory cards include a small size, a light weight, a large capacity, seismic resistance and excellent handleability. For this reason, the demand therefor as recording media for portable devices such as digital still cameras and cellular phones has grown and the semiconductor memory cards has recently also found application as recording media for consumer video recorders and professional video recorders for broadcasting.
Further, slots for semiconductor memory cards have recently become a standard feature of not only portable devices, but also stationary devices such as digital TV sets and DVD recorders, and the demand for semiconductor memory cards has further grown.
The semiconductor memory card includes a flash memory (mainly, of a NAND type) as a nonvolatile main storage memory and has a memory controller that controls the flash memory. The memory controller performs read/write control of data with respect to the flash memory in response to a data read/write command from an access device such as a digital still camera body.
The access device manages the storage area of the semiconductor memory card with a file system such as a FAT (File Allocation Table) file system. By using the file system, the semiconductor memory card can store contents data such as dynamic images, voice, and stationary images as individual files.
The increase in capacity of semiconductor memory cards is expected to result in future increase in the number of systems that write a plurality of files in parallel. For example, in access devices that perform broadcast image recording on a semiconductor memory card, a demand for a function of simultaneous recording of a plurality of programs, as in the recently developed DVD recorders, will apparently increase.
In such systems, on the access device side, data with a logical meaning (for example for each program or each contents data) are written in parallel, but on the semiconductor memory card side, a plurality of files having no logical meaning are written sporadically as a mixture. The resultant problem is that the files cannot be distinguished from each other and the write performance is degraded.
A method by which an access device writes data into a semiconductor memory card by designating a channel number has been suggested as a method for resolving the above-described problem (see, for example, WO 2009/013877).
With this method the semiconductor memory card manages a physical address of a write destination for each channel number. The access device allocates a channel number of each meaningful data (for example, each contents data) and writes the data together with the channel number. In this case, the semiconductor memory card manages a write destination for each meaningful data and therefore the degradation of write performance caused by parallel writing can be prevented.
Generally, when an access device records contents data in a nonvolatile storage device such as a semiconductor memory card, a contents file storing the contents is recorded as the contents data and various kinds of relevant information (for example, a name, a thumbnail image, a time search table, a bit rate, a reproduction time, and encryption information) attached to the contents are also recorded as contents management information files.
Further, various kinds of information attached to the entire contents, including the contents data (for example, a total contents number, a total reproduction time, a play list, and the like) are also recorded as separate contents management information files. In this case, the contents management information files are most often divided into a large number of files for each type of information that will be stored. Therefore, when one contents data is recorded, the contents of a large number of contents management information files should be updated following the recording process.
These contents management information files are used mainly when an access device reproduces the contents data that have been stored in the nonvolatile storage device. The access device looks up the contents management information files recorded in the nonvolatile storage device, retrieves and acquires various kinds of information relating to the desired contents data, and then reproduces the contents data from the contents file. The merit of such a system is that even when the number of contents data has increased to several thousands or several tens of thousands, using the contents management information files makes it possible to manage the contents data easily and perform high-speed retrieval.
However, when the power supply is cut off or the nonvolatile storage device is pulled out before the contents management information files are updated after the contents data have been recorded, the contents management information files are not updated and therefore a state is assumed in which contents data cannot be retrieved and reproduction thereof is impossible. Therefore, it is desirable that the contents management information files be updated as the contents data are recorded.
Further, in a system in which a plurality of contents data are recorded in parallel, even if the recording of a certain contents data is completed, the recording of other contents data can be continued. In such a state it is also desirable that a contents management information file relating to the contents data for which the recording has been completed be updated rapidly.
Accordingly, a method can be considered by which the degradation of write performance caused by parallel writing in a system in which a plurality of contents data are recorded in parallel is prevented by allocating a channel number to each contents file and each contents management information file.
However, where a channel number is allocated to each contents file and each contents management information file, a very large number of channel numbers are required. This results in the following problems:
(1) management of file numbers in the access device and nonvolatile storage device becomes complex, and
(2) a physical block of write destination should be ensured for each channel number in the nonvolatile storage device and storage capacity is reduced.